My 99 sle shifts really hard kind of with a slight klunk when really get on the acceleration
why is that? Does any one elses do that? and where can we find real performance parts for our bonnevilles? And how do we post pics on this website?

One thing that put 99 sle in your sig. To post pics 1st you have to find server that will host them. Then hit the Img bottom on your post then put the address in hit img. About your car how many miles since your last tranny fliud change. The other have tried pulling any codes from the computer. Most auto parts stores can do that.

First - check to see if your trans fluid is even at the right level. While your doing that you can check the color/smell of the fluid.